mDNS not working on Ubuntu core amd64

[seb2411]

Hello,

I'm testing Nextcloud Snap on a Mini PC Celeron using this config to generate the img file of Ubuntu Core:
"architecture": "amd64",
"gadget": "pc",
"kernel": "pc-kernel",
Everything seem to work well but I can't access the Nexcloud instance using nexcloud.local . It seem to me that the mdns-publisher work well but the request is sending is not processed at some point.

If I launch mdns-publisher manually I got this:

./mdns-publisher nextcloud
2017/01/15 16:54:55 Publishing nextcloud.local -> [192.168.0.16 fe80::2e0:4cff:fe68:3d16] with 60-second TTL

So I have no idea how to debug at this point and how to fix this problem or if the problem comes from nextcloud-snap or from Ubuntu Core for PC.

Thx.

[kyrofa]

If you launch it manually does it work? Are you on the same network (192.168.0.0-254) as the device?

[seb2411]

Hi @kyrofa . As I put on the first message if I launch manually I have the following message:
2017/01/15 16:54:55 Publishing nextcloud.local -> [192.168.0.16 fe80::2e0:4cff:fe68:3d16] with 60-second TTL
But is not working either. And yes I m in the same network. I can ping the box and both IP are in the same range:
192.168.0.17 for my PC
192.168.0.16 for the Nexcloud PC
The only difference is that my PC is passing by the Wifi and my NextCloud box use the LAN.

[seb2411]

If I connect my PC on the Wired network, same.

[kyrofa]

What operating system is the PC running (i.e. the thing from which you're pinging nextcloud.local)?

[seb2411]

Ubuntu 16.04.1

[seb2411]

Ok so, some updates. I was looking for Avahi (who manage mDNS) on the Ubuntu core but didn't found it. Looking on google I found this page:
http://askubuntu.com/questions/853134/avahi-samba-on-snappy-core-16-04-arm

So I installed snapweb... and entering http://snapweb.local without the port my browser show me... Nextcloud ^^ .

So my theory is that we are missing Avahi so the nexcloud snap declare the mDNS domain but there no daemon to catch it and send it over the network.

[seb2411]

@kyrofa any idea how can I try to debug this problem ?

[kyrofa]

Neither snaps use avahi; avahi is a daemon that broadcasts mDNS for its clients. Both the nextcloud and snapweb snaps directly broadcast mDNS on their own. It's interesting that snapweb.local works and nextcloud.local does not! They use pretty similar (if not identical) code for doing this.

[kyrofa]

Can I see the output of ping nextcloud.local please?

[seb2411]

Hi ! Thank for taking time to respond.

Yes it's what I understand now. The difference I can see between Snapweb and Nextcloud is the lib you are using for publishing the domain on the network.

The one used on mdns-publisher is : github.com/davecheney/mdns
The one used on Snapweb in the avahi.go file is : github.com/presotto/go-mdns-sd
The lib used in snapweb look more advanced. It seem you can specify the port of the domain for example.

I have a second bug I didn't mention before but it can help. I have 2 network interfaces on the box eth1 and eth0. And if I connect the network on eth1 and run the mdns-publisher manually is returning an error telling me there are no IP on eth0. If I connect on eth0 and execute the mdns-publisher manually is returning me the message I post before.

I didn't mention before but when I execute mdns manually and I got the message :
2017/01/15 16:54:55 Publishing nextcloud.local -> [192.168.0.16 fe80::2e0:4cff:fe68:3d16] with 60-second TTL
Is not giving me back to the terminal and is like waiting. So I don't know if it's the normal behaviour or if is waiting something, like to get confirmation of the publication of the domain who never happen.

If I ping nextcloud.local:
ping nexcloud.local ping: unknown host nexcloud.local

if I ping snapweb:
ping snapweb.local PING snapweb.local (192.168.0.16) 56(84) bytes of data. 64 bytes from 192.168.0.16: icmp_seq=1 ttl=64 time=2.45 ms 64 bytes from 192.168.0.16: icmp_seq=2 ttl=64 time=1.86 ms 64 bytes from 192.168.0.16: icmp_seq=3 ttl=64 time=1.51 ms

thx ;-)

[seb2411]

Hi @kyrofa ,

So I did a small tweak in the mdns-publisher.go replacing github.com/davecheney/mdns by the lib used on snapweb : github.com/presotto/go-mdns-sd

And it's working fine. So do you think I can try to send a PR on mdns-publisher ?

[kyrofa]

@seb2411 yes, please do! I'm curious to see the difference.

[seb2411]

I'm not sure why but I found a way to fix the problem on my box. Replacing the hostname in Ubuntu Core (/etc/hostname) by nextcloud instead of localhost.localdomain. And it's working.

So I don't know if it's necessary to do a PR on mdns-publisher.

[kyrofa]

Sounds like this issue is resolved, although I'll poke at that on the mdns-publisher project.